In scintillation counting, the radioactivity of alpha, beta, gamma, and X-ray emitters is detected and thereby the concentration of the emitters. Liquid scintillation counting comprises the addition of a specimen that emits nuclear radiation to an organic liquid mixture which in turn emits light when intercepting the radiation. The flash of light is detected, for example, by a photocell which is in a circuit that counts the flashes. The organic liquid mixture is often called a "scintillation cocktail." Generally it is comprised of an aromatic solvent for capturing the energy of the radiation, primary and secondary fluors for converting the energy to a light flash and surfactants to enable the intimate admixture of the cocktail with the specimen. See U.S. Pat. Nos. 3,939,094 and 4,124,527 for general background.
A scintillation cocktail must provide a very high degree of efficiency (number of flashes detected for number of radiated particles) for the condition under which it is to be used. Since, the amount of radio-tagged specimen is usually very small, great concern must be given to the efficiency of a scintillation cocktail when the concentration of the specimen in the cocktail is very low, say two milliliters or less of specimen per eight milliliters of cocktail.
U.S. Pat. No. 3,939,094 contains teaching regarding liquid scintillation cocktails containing mixtures of polyethoxylated polyoxypropylene surfactants and teachings regarding liquid scintillation cocktails containing a single polyethoxylated polyoxypropylene surfactant. It is specifically taught that for single surfactant-type cocktails, the polyethoxylated polyoxypropylene materials should have about 32 to 40 polyoxypropylene groups or less desirably 18 to 25 polyoxypropylene groups and comprise 10 to 30 percent by weight polyoxyethylene. The preferred surfactant comprises Pluronic L72 with Pluronic L42 being somewhat less preferred and both being considered superior to Pluronic L62.
Surprisingly, the applicants have found that for very small sample specimen quantities, superior liquid scintillation cocktails can be batched using a single polyethoxylated polyoxypropylene surfactant that is not one of those taught to be preferred or even acceptable when used by itself in U.S. Pat. No. 3,939,094.